Electric induction furnace process



March 25, 1930. A. E. GREENE 1,751,856

ELECTRIC INDUCTION FURNACE PROCESS Original Filed March 25, 1921 mhh)! 5t \7 52 \8 53 19 S4 2o 55 2 56 22 57 23 lNVENTORg Patented Mar. 25, 1930 PATENT OFFICE ALBERT E. GREENE, OF SEATTLE, WASHINGTON ELECTRIC INDUCTION FURNACE PROCESS Application filed March 25, 1921, Serial No. 455,601. Renewed May 12, 1923.

My present invention relates to electric induction furnaces and more particularly to a new method of operating them to cause circulation of the molten metal thru the channels while heated inductively by current therein.

The use of relatively small channels in refractory material connecting with chambers of larger size with a view to heating the metal by current induced in the small channels has been suggested and circulation of the metal from the small channels into the large chambers has been proposed both by electro-magnetic effects producing circulation and also by circulation due to the tendency of heated metal to rise and be replaced by colder metal.

My invention rests on certain discoveries relative to the construction and operation of induction furnaces in which the secondary circuit is in a channel parts of which consist of ducts which are closed except on their ends where they connect with the adjoining parts of the channel. I discovered that under the influence of sufficient hydrostatic pressure or fluid pressure on the molten metal in such a duct, more current could be made to flow thru the metal therein than could be made to flow thru an open top channel. And I made the further discovery that this increased heating means could be advantageously applied by causing forced flow of the metal thus heated whereby it is forced out of the duct part of the channel and into the adjoining part of the channel or chambers with which it connects.

Those familiar with induction furnace op eration are aware of the action known as the pinch effect. This action is the result of excessive current within a channel containing metal forming part of the single turn secondary circuit of an induction furnace. It is a mechanical effect due to the tendency of the current to close in upon itself or to squeeze the conductoras it were. It is an effect which can be overcome, provided the hydrostatic or fluid pressure in the metal is sufficient to prevent the disturbing pinch effect. This pinch effect is most evident in small open-top channels in induction furnaces where the metal level is not sufficient to keep the metal in place against the disturbing influence of the current passing thru it. The result of it is to partially or completely break the circuit, after which the current is thereby diminished and consequently the metal flows back and tends to assume its former level. By placing the special duct, closed except on its ends, well below the metal level in the adj oining parts of the circuit, a much greater amount of current is necessary to cause this pinching effect on the metal in the duct. I discovered, that under the influence of a sufficiently increased hydrostatic pressure on the metal within the duct, I could cause much greater current to flow and that even tho I caused suiflcient current to flow so that I actu' ally observed or heard the pinching and consequent arcing within the tube, yet this did not interfere" with the heating operation. Thus I discovered that even tho the effect was such as to cause arcing within the tube yet by means of the step of moving the metal thru the tube this heating effect was taken advantage of.

My invention consists in the method and apparatus for heating fluid metal in ducts closed except on their ends and opening into adjoining parts of a larger chamber or cham bers below the normal metal level therein and in causing the forced flow of metal thru these ducts, meantime inducing current in the metal in the ducts for heating purposes. My invention further consists in utilizing large current densities in metal in ducts forming part of a single turn circuit around a magnetic core of an induction furnace and mean time forcing the metal to move within the ducts under hydrostatic pressure greater than that due to a head of metal equal to the height of the metal inside the duct, and doing this even tho arcing takes place within the duct. The use of straight ducts, the horizontal arrangement of these and the location of the ducts with their open ends connecting with larger chambers at the lower parts of the latter, and the direction of rocking movement of the furnace in relation to the direction of the ducts, these are all important features of my invention.

My present invention, however, accomplishes circulation of melted metal thru the small ducts connecting with larger chambers in an entirely different and very simple manner,namely simply by rocking the furnace so as to raise one large chamber above the level of the other and so cause the metal to flow thru the intermediate channels into the lower large chamber and to become heated or take up heat in this transfer, and as soon as the greater part of the metal has been transferred in one direction the procedure is reversed.

One purpose of my present invention is to heat metal in the manner just described. Another purpose is to cause the melting of cold metal placed in the large chambers or in one of them by means of the circulation and heating effect of the current induced in the metal in the channels while moving the furnace to change the relative elevation of the two larger chambers. A further object of my invent-ion is to provide a simple and inexpensive method of melting and heating metals.

One special feature of my invention relates to the construction of the connecting channels, and more particularly the use of straight channels for these parts which may be easily made and repaired.

Another feature relates to the rocking or tilting of the furnace to alternately raise and lower one chamber above another so as to cause circulation of the metal.

Another feature relates to the construction of the main chambers or charging crucibles; more particularly to produce an eflicient and simple furnace.

I will now describe a furnace embodying my invention and specific features thereof, as well as the method of operating it.

In the drawings annexed I have shown a construction of furnace adapted to carry out my present invention.

Fig. 1 is a sectional elevation of a two chamber furnace having connecting channels, a magnetic core, and other parts.

Fig. 2 is a plan view of this furnace shown in Fig. 1, with the left hand chamber cover removed to give a view down into the left crucible chamber. 7

I will now describe my invention with particular reference to the drawings annexed.

Referring to the two figures which represent different views of the same furnace I have for convenience of reference numbered the various parts and I will touch upon each of these numbered parts before further describing the invention. 1 is a View of the electrode which extends thru the roof 2 into the chamber 3. 4 is the refractory lining forming the main chamber 3 and held in the shell 5 of suitable plate material. 6 is a reference line the metal surface in chamber 3 in one stage of operation. 9 is the reference line to the metal at 8.' 10 is one opening into the lower part of the chamber 3. 11 is a spout. 12 is a view showing the elevation of one of the small channels connecting the lower part of chamber 3 with chamber 38. 13 is the lower part of the magnetic core of the furnace held in the supporting structure 14 which is rocker shaped permitting the furnace to roll or tilt on a track represented by 15. 16 shows the relative position of the track when the furnace is in the normal position with the connecting channels about level. 17 shows one end of one of the parts of the shell which might be a boiler head. 18 is the adjoining shell. 19 is the roof shown in section at 2. 20 represents one of the connecting channels and there are four in all. 21 is an extension of the connecting channel 20 and may be used either to clean the channel 20 with a rod or to tap the furnace or to plug the ends of the channel 20. 22 represents the bottom outline of the chamber 3. 23 represents an electrode in chamber 3. 24 represents the next connecting channel and 25 the corresponding opening to the outside like 21. 26 is another electrode. 27 is a third connecting channel between chamber 3 and chamber 38. 28 is a spout and similar spouts may be attached where each of the utlet channels like 21 comes out. 29 is the/outlet channel thru the spout 28. 30 is the third electrode. 31 is the fourth outlet channels or tap hole and 32 is the fourth connectin g channel. 33 is the top end of the magnetiocore. 34 is the other end of the shell from 17. 35 represents one of the windings on the core which is a three phase core. 36 represents the top part of the core. 37 represents the cover to the left hand chamber 38. 39 is an elevation line indicating the level of metal in the chamber 3 in one posit1on of thefurnace. 41 shows another metal surface level when the furnace is tilted. 42 is an elevation line to show the difference in level from the bottom of the chamber 38 trwhich this line 42 leads. 43 shows a pin of a cylinder connecting rod 44 serving to move the furnace. 45 is an outlet channel similar to 21. 46 is the end of the connecting channel near chamber 38. 47 is a cylinder for tilting the furnace. 48 is an elevation line to show the relative position of the furnace when tilted over. 49 is the other end of line 16. 50

represents another winding on the magnetic core. 51 is the end of one of the furnace shell sections. 52 is the corresponding shell plate adjoining. 53 is the opening of channel 20 into chamber 38. 54 is the bottom of chamber 38, the cover 37 being removed here. 55 is a winding on one upright leg of the core, this leg being shown in dotted line at 56. 57 is the opening of the next channel into 38. 58 is the center core leg. 59 is the winding on 58. 60 is the opening of the third channel into 38. 61 is the third leg of the core and 62 the coil thereon. 63 is the left end of a section line, the upper figure being a section 011 this line 63--63 64 is the opening into 38 of the fourth connecting channel. 65 is the end of the shell.

The operation of the furnace consists in providing molten metal, for example brass in the chamber of the furnace, for example it may be poured into chamber 3 and will fill the connecting channels and enter chamber Altho I have shown an electrode in the chamber 3 the method of melting charge to fill the channels using an are or resistance is described and claimed in my separate application for patent Sr. No. 406,894, filed Aug. 30, 1929.

When the connecting channels are filled with molten metal and the metal extends into the main chambers 3 and 38, then the current may be induced in the molten metal secondary circuits around the legs of the transformer cores by connecting the primary windings with the power circuit. The control of current induced may be by connecting the proper number of turns of the transformer windings with the supply circuit of given voltage, for example as described in my U. S. application for patent Serial No. 207.966 filed Jan. 3, 1913. The channels are relatively small and with metal well up in the main chambers suflicient head is available to permit very large current in the metal in these connecting channels such as 20. For example the channel may be of about 1" cross sectional area and 25" long and hold roughly 8 or 10 pounds of metal so that the four channels would hold some 40 pounds, while each main chamber like 3 might hold some 80 pounds, thus making a total charge of 200 pounds. This amount would not be necessary for operation nor would it be the maximum charge but these figures are given merely by way of making the operation clear and easy to understand. It will be seen that a very slight movement of the furnace on the rockers 14 will serve to transfer all the metal in the channels, that is some 40 pounds, from one part of the furnace into another; yet the necessary head in the main chambers may be maintained. By very high current in the channels the metal will heat quickly and by tilting the furnace slightly this metal will run into the lower chamber and its place be filled by colder metal from the higher chamber; and then the furnace may be tilted in the other direction to reverse the relative elevations of the two chambers and cause the metal to flow back the other way. This procedure will rapidly heat all the metal in the Whole furnace. Whenever the metal reaches a desired temperature then the furnace power may be regulated to merely make up for radiation and the rocking of the furnace may be kept up regularly, or intermittently or stopped until needed.

The above described method of circulating the heated metal from the connecting tubes or ducts may be used to heat and melt cold charge in either or both the main charge chambers 3 and 38. Cold scrap metal may be charged in either or both of these and then the heating and circulating process carried out as already described until the charge is all raised to the desired temperature.

Fig. 1 shows the effectit e head gained by tilting the furnace. Suppose practically all the metal except just enough to cover the connecting channel openings is passed from chamber 3 into 38 and then suppose the fur nace is tilted toward the spout side so as to raise chamber 38 above chamber 3. In the Fig. 1 I have shown a line marked 6 for reference which shows the top level which the metal in 38 might have with a tilt forward of only about 5 degrees of are beyond the normal upright position of the furnace and the distance between the line 6 and the line 9 shows the eflective head which might result. It will be noted that the heavy line 15 would represent the horizontal and the metal surface in 38 would assume a parallel surface along the line 6. The metal would flow thru the connecting channels and equalize the head in both parts of the furnace.

By tilting the furnace until practically all metal is in chamber 3 and then raising cham ber 3 above 38 by tilting the furnace until the line 48 represents the horizontal, there would be a still greater head produced, this head being represented by the difference in elevation between the two (then horizontal) lines 39 and 42, that is by the distance 40. In the degrees of tilt the difference of head can be controlled. However the tilting may be kept up so that only small amounts of metal move from one main chamber to the other.

The tilting or rocking of the furnace may be by hand, for example by hand control of the valve operating a double acting hydraulic cylinder as shown at 47, or the furnace may be tilted by any hand operated mechanism. It also may be operated by a motor and connecting rod in place of the hydraulic cylinder, and the length of stroke or degree of tilt may be controlled and also the rocking may be kept up continuously as long as desired.

The furnace is intended to be properly heat insulated and metal may be melted untll the chambers are practically filled.

The metal may be tapped from the furnace by opening a hole like that at 9 or 29. The

furnace may be tilted to control the flow thru Well suited for iron and also steel and copper and high melting metals.

The apparatus and process of this invention is not limited to the melting or heating of metal but may be used for the metallurgical treatment of metal or of other material in the furnace and these uses constitute separate inventions in their details.

It is also understood that the invention may be practised in other construction of furnace than that shown in the annexed drawings so long as the essential features necessary to the present invention are maintained. The connecting channels may be of round or square or other cross section. The main chambers may be of different shape from those shown and altho I have'specifically described and claimed certain of these improved features in other applications they do not constitute the present invention. Likewise I may use a single phase furnace or apolyphase furnace and the arrangement of cores and coils may be varied without getting away from the essential features of my present invention.

It is to be understood that my use of the term large current in this specification is relative, and that altho the current density may be great, the actual current thru a given conduit, expressed in amperes may not be very great. This matter will be better understood when it is noted that the cross sectional area of a conduit may be less than 1 square inch.

One advantage of my present invention is that the heating may take place in a small area conduit with high current density in the metal but only small area whereby the parts of the furnace may be built more efiiciently and closer together.

What I claimis:

1. The methdd of treating molten metal by causing it to pass through a constricted area duct closed except 011 its ends and having its ends opening into adjoining parts of the channel of an induction furnace larger than the ducts and at a part of said channel below the metal level therein and while forcing it through said conduit heating it by passing induced current through the metal therein.

2'. In an electric induction furnace, in combination, a furnace body having a channel for the bath, a primary transformer element, the bath in said channel serving as a secondary and being heated by the current in-v duced therein, the said channel comprising ducts of small cross sectional area closed except on their ends and having their ends opening into the larger parts of the channel below the normal metal level therein, and means for causing the furnace body to rock, at such I ends where they join the larger parts of the channel at the lower part thereof, a primary transformer element, the bath insaid channel serving as a secondary and being heated by the currents induced therein, and means for causing the furnace body to rock at such intervals and in such manner as to stir the bath.

4. In an electric induction furnace, in combination, a furnace body having a channel for the bath, a charging opening, a plurality of symmetrically arranged pockets for the charge, and the channel comprising ducts closed except at their endsand of relatively small cross sectional area with respect to other parts of the channel and opening into the other parts atthe lower elevation thereof, and a primary transformer element, the bath in the channel serving as a secondary and being heated by the induced currents therein.

5. In an electric induction furnace, in combination, a furnace body having a horizontal channel for the bath, a plurality of pockets for the .charge,-commun1cating passages of smaller cross sectional area and closed except at the ends between said pockets and opening into said pockets at the lower part thereof, and a pouring passage leading to a spout, means for causing the furnace body to rock in the direction of said passages,

.and means for tilting the furnace body in the direction of one of said passages to pour the charge, whereby the lowest part of the channel has an outlet when in poring position.

6. In an electric induction furnace in which part of the induction channel is straight, an opening thru the refractory lining of the chamber into said channel whereby a bar may be inserted into said straight section.

7 In an electric induction furnace a plurality of straight channels forming parts of the induction circuits, and. openings into said channels thru the outer lining of the fun nace, said openings being of approximately the same cross sectional area as the channels.

8. In the operation of an induction furnace comprising a channel part of which is a relatively small area duct closei except at its ends where it joins and opens into the other part of the channel, the method which consists in increasing the current density sufficiently to cause arcing within the duct and meantime forcing movement of the metal thru the duct.

In witness whereof I hereunto subscribe my name this 22nd clay of March, A. 1D. 1921.

ALBERT E. GREENE, 

